Many known battery-powered medical devices, such as semi-automatic external defibrillator (“AED”) devices, rely on batteries to power electronics of the device, and, in the case of the AED device, to administer electric shocks to patients. For example, AED devices are used to provide electric shocks to treat patients for a variety of heart arrhythmias. The AED provides relatively high-level shocks to a patient, usually through electrodes attached to the patient's torso, to convert, for example, ventricular fibrillation to a normal sinus rhythm.
Studies have demonstrated that survival rates are high when defibrillation treatment is administered within the first few minutes following cardiac arrest. The likelihood of successful resuscitation, however, decreases by approximately 10 percent with each minute following sudden cardiac arrest. After ten minutes, very few resuscitation attempts are successful. Thus, it is advantageous to construct an AED that includes a reduced size and weight to be conveniently portable. One way to reduce the size and weight of the AED is to reduce the size and weight of the battery system.
For a defibrillation pulse to be effective in terminating cardiac arrhythmia, however, sufficient energy must reach the heart, through muscle, bone, organs and other tissues. In addition, the battery system of the AED is often called upon to power non-essential functions of the AED such as powering at least a portion of the electronics of the AED, for example, to perform AED self-tests, sound AED enunciators and visually indicate status. Thus, the battery system preferably includes enough energy to power the non-essential functions over a period of time, for example years, and still be able to deliver a high dose of energy when needed. A known solution is to include a bigger power supply in the battery system to handle these needs, which thus increases the size and cost of the AED. Another solution is to more frequently replace the power supply in the battery system, which may increase cost of operating the AED and increase the amount of maintenance that the AED requires.
Thus, there is a need for an improved battery system for a medical device such as an AED.